1. Field of the Invention
The present invention relates to a liquid fuel and a fuel cartridge adapted for a fuel cell and also relates to a fuel cell.
2. Description of the Related Art
In a fuel cell, fuels such as hydrogen and methanol are electrochemically oxidized within a cell so as to convert the chemical energy of the fuels directly into an electric energy so as to take out the electric energy. Therefore, the fuel cell is free from the generation of the air pollutants such as NOx and SOx, which are caused by the combustion of the fuels in a thermoelectric power plant, and, thus, attracts attention as a supply source of a clean electric energy.
Particularly, the direct liquid fuel cell is said to be capable of miniaturization and, thus, vigorous research is being carried out on such fuel cells in an attempt to develop a portable fuel cell. Various types of direct liquid fuel cell are known to the art, including a fuel cell of the liquid fuel supply type utilizing capillary force or channel plate. An alcohol, formic acid or an aqueous solution thereof is used as the liquid fuel of the fuel cell. On the other hand, in the portable fuel cell, how to supply the fuel to the fuel cell is an important factor for achieving continuous power generation. As one of the fuel supply methods, it is known to the art to design the fuel cell to include a fuel cell body and a fuel cartridge that can be connected to the fuel cell body. In this case, the fuel cell can perform continuous power generation by replacing the fuel cartridge.
In order to enable the fuel cell described above to perform continuous power generation, it is crucial to use the fuel cartridge. On the other hand, in the direct liquid fuel cell, the fuel is supplied directly to the power generation element, i.e., the membrane electrode assembly (MEA), giving rise to the defect that the direct liquid fuel cell tends to be highly affected by the impurities contained in the fuel. The fuel itself is synthesized and prepared by various methods, with the result that it is possible for many impurities to be contained in the fuel. Also, it is preferable for the fuel used in the fuel cartridge to have a high concentration in order to increase the volume energy density of the fuel. However, if the fuel concentration is increased, the impurities tend to enter the fuel more easily.
Each of Jpn. Pat. Appln. KOKAI NO. 2005-5155 and Jpn. Pat. Appln. KOKAI NO. 2005-38803 relates to a fuel container for a fuel cell, comprising a container body having a hermetic structure and a valve mechanism for controlling the supply of the fuel from within the container body. It is disclosed in each of these patent documents that the constituting members of the fuel container that are in contact with the fuel are formed of a nonmetallic material so as to avoid elution of metal ions into the fuel housed in the fuel container.
Also, Jpn. Pat. Appln. KOKAI NO. 2001-93558 relates to a direct alcohol fuel cell, particularly, to a fuel permeation evaporation type fuel cell. It is reported in this patent document that a surfactant is added to the fuel in order to improve the permeability of the fuel and, that a discriminating agent, i.e., an organic material having a color or a odor, is also added to the fuel in view of the safety. However, in the fuel cell reported in this patent document, the fuel can permeate into a porous body by utilizing the capillary phenomenon so as to be evaporated. Such being the situation, it is impossible for the additives noted above to be evaporated and accumulated in the MEA.
Further, Jpn. Pat. Appln. KOKAI NO. 2001-93558 quoted above teaches that a surfactant, a coloring dye, a low-freezing liquefying agent, etc. are added to the fuel for the fuel cell.